An inverter control device for electric compressors is provided with circuits, such as a power-supply monitoring circuit to detect a voltage reduction of a main power-supply at low-voltage side by a microcontroller placed at high-voltage side of a circuit of which low-voltage side is isolated from high-voltage side so that the control works well even when the voltage is unstable.
For example, Patent document 1 discloses a power-supply voltage monitoring circuit, wherein an input power-supply voltage is imported into a microcomputer, etc., at regular time intervals to be determined so that an outage program is executed by extending the reduction of voltage input to a calculating means by combining a predetermined calculating means, resistive elements and capacitors as detecting an instant outage without overlooking.